What is the grammar rule for the preposition after the word free? Why do we say free of impurities but free of charge?

  • Welcome to English SE, @teacher! I'm not sure what you're asking here; why "impurities" is plural but "charge" is not, when following "free of"?
    – Pops
    Feb 4, 2011 at 15:28

2 Answers 2


The "charge" vs. "impurities" difference you actually seem to be asking about is nothing to do with the preposition as such; it's to do with "charge" being a "mass noun", so not calling for pluralization, and "impurity" being a "count noun", which it's appropriate to pluralize here.

This distinction is the same one as produces the "less vs. fewer" dichotomy.


There are other prepositions you could use with "free" as well:

  • I am free from two till four this afternoon.
  • I would like to be free of this burden.
  • A soft drink comes free with purchase.
  • You are free to do what you want.
  • The offer is free while supplies last.
  • Hang on, I'll be free in five minutes.
  • I'm free at last!

I could go on ...

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